This invention relates in general to shaft packing constructions and in particular to a new and useful liquid packing for sealing the shaft clearance between a low pressure zone and a high pressure zone.
A liquid packing for sealing between high and lower pressure seal zones of a shaft is known through German Pat. No. 21 53 560. In this prior art packing, an annular pumping chamber in which the pressure of the sealing liquid is augmented by a centrifugal force, is provided between the bore for supplying the sealing liquid and the sealing gap at the high-pressure side, and the constant pressure of the supplied sealing liquid is only slightly higher than the pressure in the high-pressure zone. In connection with the chamber provided at the operating end of the sealing gap at the high-pressure side, at any speed, the pumping effects of the pumping chambers at the two sides of the high-pressure sealing gap compensate for each other, so that due to the pumping effect, a liquid pressure substantially exceeding that of the operating gas is maintained in the sealing gap at the high pressure side. With the machine at standstill, the higher pressure prevents the operating medium from penetrating into the packing, and also allows only a small leakage of sealing liquid into the high pressure zone.
What is disadvantageous in this prior art packing is that in the partial sealing gap at the high-pressure side, the sealing liquid is close to stagnant, so that the entire friction heat produced in this partial sealing gap and the adjacent centrifugal packing at the high pressure side must be dissipated indirectly, through the housing parts and the shaft bushing. With high circumferential speeds in the sealing gap, the narrow sealing gaps intended to reduce the leakage at standstill are not sufficient. In addition, during normal operation, the front face at the high pressure side of the double bushing surrounding the rotating impeller is exposed to the higher pressure from the pumping chamber, which produces axial forces acting on the front face of the housing and is disadvantageous with a floating double bushing.